A 52-year-old man presented to the emergency department with a 2-month history of worsening dyspnea which intensified during the last 3 days. On physical examination, his blood pressure was 119/68 mm Hg, his pulse rate was 99 beats per minute, and his respiratory rate was normal. An electrocardiographic study (Fig. 1A) and computed tomographic (CT) angiography of his chest (Fig. 1B) were performed at the time of hospital admission.
